Cardiac content and plasma concentration of atrial natriuretic polypeptide (ANP) in spontaneously hypertensive rats...

The cardiac content and plasma concentration of atrial natriuretic polypeptide (ANP) in hypertensive rats were measured by using radioimmunoassay for ANP. The animals used in this study were young (5-week-old) and adult (12- to 14-week-old) spontaneously hypertensive rats (SHR), stroke-prone SHR (SHR-SP) and normotensive control Wistar-Kyoto rats (WKY). Most immunoreactive ANP in the cardiac extract of the hypertensive rats (both SHR and SHR-SP) was found to be predominantly gamma-form as well as that of WKY. Cardiac ANP content in adult SHR and SHR-SP was significantly lower than in adult WKY (p less than 0.01), although there were no differences among three groups in young rats. Similar tendencies were also observed for plasma ANP concentration. The level of plasma in adult hypertensive rats was significantly lower or tended to be lower than in adult normotensive rats. Furthermore, a high negative correlation was present between blood pressure and cardiac ANP content (r = 0.748, p less than 0.01) and between blood pressure and plasma ANP concentration (r = 0.608, p less than 0.01) in all adult rats but there were no such relationships in young rats. The present study suggests that atrial natriuretic polypeptide may contribute to the pathogenesis or maintenance of high blood pressure in the genetic hypertensive rats.